Rationale for the DryRun guard on callbacks.RowQuery

[emetsger]

Your Question

TL;DR: can you tell me why callbacks.RowQuery is not supported in dry run mode? Is there a possibility (I'm happy to contribute a PR) that it could support dry run mode?

Use case

My use case is to use DryRun to capture table creation DDL with Migrator running in dry mode. A promising approach has been to implement a custom logger to capture the generated SQL to an io sink (I've also tried wrapping a Dialector) but otherwise leave the target database's state alone (i.e. dry mode).

Blocker

However, this approach seems incompatible with callbacks.RowQuery, which guards the write to Statement.Dest with a if !db.DryRun block†. The presence of this guard implies that callbacks.RowQuery is generally incompatible with dry mode, and I'm wondering if you can tell me why that is? I just don't have enough experience with Gorm to reason about why that might be the case.

†(this actually causes a panic because the finisher_api's func (db *DB) Row() *sql.Row will return a nil *sql.Row instead of populating a *sql.Row with an error)

The document you expected this should be explained

This is a pretty low-level question, and might be my ignorance. So I don't expect it to be documented. For reference I did read the following:

• https://gorm.io/docs/session.html#DryRun
• https://gorm.io/docs/write_plugins.html
• https://gorm.io/docs/migration.html

Expected answer

That callbacks.RowQuery is compatible with dry run, you just need a PR and some tests :)

[a631807682]

TL;DR: can you tell me why callbacks.RowQuery is not supported in dry run mode? Is there a possibility (I'm happy to contribute a PR) that it could support dry run mode?

Since Row does not return grom.DB, we do not support it, but in any case we should not panic.

https://gorm.io/docs/sql_builder.html#ToSQL https://gorm.io/docs/session.html#DryRun

When (*sql.Row).Scan has err, it returns err first. At present, I don't know if there is any way to handle it without changing the api.

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